Valves, such as pressure regulating valves or diaphragm valves, have a fluid-free area and an area through which the medium flows. As a rule the two areas are separated from one another by a diaphragm.
Pressure regulating valves, such as overflow valves and pressure-retaining valves, which are installed in pipeline systems, serve to maintain work-conditioned and system-conditioned pressures at a constant level. They make it possible to compensate for pressure pulsations and to break down pressure peaks. Pressure-reducing valves, which likewise fall within the group of pressure regulating valves, make it possible to reduce the system pressure to a predetermined value.
In such pressure regulating valves, an actuator unit, which mostly contains a spring, a spindle and a spring plate, is arranged in the fluid-free area. The spindle is generally guided through a bearing in the housing upper part. For a reliable functioning of such a valve it is therefore absolutely essential that the fluid-free chamber is not contaminated by the medium. If fluid were to leak and penetrate into the fluid-free chamber, then it would affect the functioning of the actuator unit and the valve would lose its functional reliability. The media in such pipeline systems are generally corrosive whereby the impurities which are worn away and carried along would likewise be brought by the leak into the fluid-free chamber and contamination of the actuator unit would be unavoidable. In the case of chemicals which are harmful for the environment, there is also the danger that the chemicals pass into the environment via the fluid-free chamber.
The fact that such valves are completely closed and out of sight means that it is not possible to observe whether the medium has already entered into the fluid-free area or chamber which means an early detection of a leak is not possible.
Diaphragm valves are also likewise affected by the aforementioned disadvantages since they likewise have two areas, a fluid-flowing and a fluid-free area, which are separated by a diaphragm.
Fitting an inspection glass would only allow any penetration of the medium into the fluid-free chamber to be detected when a clearly visible amount of the medium had penetrated into the fluid-free area. This would in most cases be too late to prevent a valve failure. The valve would then be difficult to repair with a low expense or few replacement parts and also the functional reliability would no longer be satisfactorily guaranteed. The probability of a complete replacement of the valve would be very high which would result in high costs.
Diaphragm valves are by way of example used for shutting off pipeline systems. If now too much contamination or decomposition by the medium is already present in the fluid-free area so that the spindle unit mounted therein no longer functions but this cannot be detected from outside, and the operating member such as by way of example a hand wheel is nevertheless still rotatable, it cannot be recognized that the diaphragm valve can no longer be closed. The pipeline system is then nevertheless still fluid-flowing as it is assumed that the diaphragm valve had been closed. Such a false assumption can lead to greater damage by way of example when dismantling a component if the pipeline system is fluid-flowing.
The WO 90/15977 discloses a valve which has a leakage detector which is connected to a control. By detecting a leak as a result of medium entering into the fluid-free chamber the detector forwards a signal to the control which switches off the pump for conveying the medium.
The drawback with this system is the high technical expense for detecting a leak. As a result of the electronic components which are required, a valve of this kind is expensive and liable to break down.